On Fri, Sep 3, 2010 at 3:50 PM, Benjamin Root <ben.root@ou.edu> wrote:

Here is a fun one...

import numpy as np

a_2d = np.random.random((3, 5)) b_1d = np.random.random(5) b_2d = np.vstack((b_1d, b_1d, b_1d))

a_ma_2d = np.ma.masked_array(a_2d, mask=(numpy.random.random((3, 5)) < 0.25)) b_ma_1d = np.ma.masked_array(b_1d, mask=(numpy.random.random(5) < 0.25)) b_ma_2d = np.ma.masked_array(b_2d, mask=(numpy.random.random((3, 5)) < 0.25))

# a**b without broadcasting (works) print a_2d**b_2d

# a**b with broadcasting (works) print a_2d**b_1d

# a_ma**b_ma without broadcasting (works) print a_ma_2d**b_ma_2d

# a_ma**b_ma with broadcasting (works) print a_ma_2d**b_ma_1d

# a**b_ma without broadcasting (works) print a_2d**b_ma_2d

# a**b_ma with broadcasting (FAILS) print a_2d**b_ma_1d Traceback (most recent call last): File "<stdin>", line 1, in <module> File "/home/bvr/Programs/numpy/numpy/ma/core.py", line 3697, in __rpow__ return power(other, self) File "/home/bvr/Programs/numpy/numpy/ma/core.py", line 6043, in power m |= invalid ValueError: invalid return array shape

# Now, test broadcasting of the other side of the operator c = np.random.random(5) c_ma = np.ma.masked_array(c, mask=(np.random.random(10) < 0.25))

# c**b_ma with broadcasting (works) print c**b_ma_2d

# c_ma**b with broadcasting (FAILS) print c_ma**b_2d Traceback (most recent call last): File "<stdin>", line 1, in <module> File "/home/bvr/Programs/numpy/numpy/ma/core.py", line 3693, in __pow__ return power(self, other) File "/home/bvr/Programs/numpy/numpy/ma/core.py", line 6043, in power m |= invalid ValueError: invalid return array shape

So, this fails if we broadcast the masked array portion of a power expression and the other value is a ndarray. Note, the same also occurs if we broadcast a masked array in order to raise it to powers indicated by an ndarray.

Took me the longest time to nail this one down... Ben Root

Btw, I have filed a bug report on this: http://projects.scipy.org/numpy/ticket/1606#comment:1 Ben Root